1. Statement of the Technical Field
The inventive arrangements relate to Microelectromechanical System (“MEMS”) and methods for forming the same, and more specifically to micro-scale spring suspension systems for MEMS devices.
2. Description of the Related Art
MEMS is a technology of very small devices between 2 micrometers to 2 millimeters in size. The MEMS devices can include one or more components between 1 to 100 micrometers in size. Conventional MEMS devices are fabricated using molding techniques, plating techniques, wet etching techniques, dry etching techniques, and/or Electro Discharge Machining (“EDM”) techniques. Various materials can be used to create the MEMS devices. Such materials include silicon, polymers, metals and ceramics.
Radio Frequency (“RF”) filters typically occupy a relatively large amount of real estate in an RF system (i.e., >25%). RF filters often comprise varactor devices, such as Gap Closing Actuator (“GCA”) varactors. GCA varactors generally operate on the principle of electrostatic attraction between adjacent interdigitating fingers of a drive comb structure and a movable truss comb structure. That is, motion of the truss comb structure can be generated by developing a voltage difference between the drive comb structure and the truss comb structure. The voltages applied at comb structures are also seen at the interdigitating fingers, respectively. The resulting voltage difference generates an attractive force between the interdigitating fingers. If the generated electrostatic force between the fingers is sufficiently large to overcome the other forces operating on truss comb structure (such as a spring constant of a resilient component), the electrostatic force will cause the motion of the truss comb structure between a first interdigitated position (resting position at a zero voltage difference) and a second interdigitated position (position at a non-zero voltage difference) among a motion axis. Once the voltage difference is reduced to zero, a resilient component (e.g., a spring) restores the position of the truss comb structure to the first interdigitating position.
In such a varactor device, there is tradeoff between the mechanical spring stiffness and the actuation of the voltage required to move the truss comb structure. Specifically, the stiffer the spring the higher the voltage needed to move the truss comb structure. Therefore, the actuation voltage can be dramatically lowered by lowering the resilient component (e.g., a spring) stiffness. However, this makes the system more susceptible to external vibrations which may cause damage to the circuit and/or cause undesired performance. In industry, the problem is usually avoided by making the resilient component (e.g., a spring) sufficiently stiff and adding boost electronics to get the desired high voltage. This solution is undesirable because (1) high voltage electronics can be dangerous in certain applications (e.g., in-vivo biomedical applications) and (2) the boost electronics occupy a relatively large amount of space on an RF circuit board.